﻿using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Windows.Data;

namespace AppToolkit.WPF.UI.Converters
{
    /// <summary>
    /// Allows converting a <see cref="DateTime"/> value to string or the other way round.
    /// </summary>
    public class DateTimeConverter : IValueConverter
    {
        private const string NotANumber = "<n.a.>";
        /// <summary>
        /// Format string to be used for rendering the <see cref="DateTime"/> value.
        /// </summary>
        public string FormatString { get; set; }

        #region IValueConverter Members

        /// <summary>
        /// Converts a value. 
        /// </summary>
        /// <returns>
        /// A converted value. If the method returns null, the valid null value is used.
        /// </returns>
        /// <param name="value">The value produced by the binding source.</param><param name="targetType">The type of the binding target property.</param><param name="parameter">The converter parameter to use.</param><param name="culture">The culture to use in the converter.</param>
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            var typedValue = value as DateTime?;
            if (typedValue == null || !typedValue.HasValue)
            {
                return NotANumber;
            }
            return (!string.IsNullOrEmpty(this.FormatString)) ?
                    typedValue.Value.ToString(this.FormatString) : 
                    typedValue.Value.ToString(CultureInfo.InvariantCulture);
        }

        /// <summary>
        /// Converts a value. 
        /// </summary>
        /// <returns>
        /// A converted value. If the method returns null, the valid null value is used.
        /// </returns>
        /// <param name="value">The value that is produced by the binding target.</param><param name="targetType">The type to convert to.</param><param name="parameter">The converter parameter to use.</param><param name="culture">The culture to use in the converter.</param>
        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            var typedValue = value as string;
            if (typedValue == null || string.CompareOrdinal(typedValue, NotANumber) == 0)
                return null;
            
            DateTime date;
            if (DateTime.TryParse(typedValue, out date))
                return date;
            return null;
        }

        #endregion
    }
}
